Ferrofluidic cooling and acoustical noise reduction in magnetic stimulators

ABSTRACT

A ferrofluid chamber has a housing that is adapted to be coupled to a component that generates a magnetic field. A ferrofluid may disposed within the housing for cooling the component via convection of the ferrofluid that is induced by the magnetic field.

REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.11/130,657, filed May 17, 2005, entitled “FERROFLUIDIC COOLING ANDACOUSTICAL NOISE REDUCTION IN MAGNETIC STIMULATORS”.

FIELD OF THE INVENTION

The invention relates to the field of magnetic stimulation.Specifically, the invention relates to cooling a magnetic stimulationdevice. In addition, the invention relates to acoustically insulatingsuch a magnetic stimulation device.

BACKGROUND OF THE INVENTION

Magnetic devices are used in many applications, such as in magneticstimulation devices, speakers and so forth. Magnetic devices tend togenerate heat because of resistive losses in the coil(s) that generatemagnetic fields(s), and the amount of heat generated is proportional tothe amount of power consumed by the device. Thus, high-voltage magneticdevices that consume large amounts of power, such as those used inmagnetic stimulation therapy, can become very hot when in operation. Theenvironment in which the magnetic device operates—or the operatingcharacteristics of the device itself—may dictate that the device operateunder a certain temperature threshold. For example, in magneticstimulation therapy, the temperature of a magnetic stimulation deviceused to generate a therapeutic magnetic field should be kept belowapproximately 41.5° C. to stay within certain regulatory requirements(e.g., FDA guidelines). If a magnetic stimulation device is to beoperated at temperatures exceeding 41.5° C., such regulatoryrequirements dictate that the device manufacturer and/or healthpractitioner must meet additional guidelines to prove that operation ofthe device is safe. These additional requirements increase complexity ofoperation and overall cost, and are best avoided when possible.

Conventionally, a magnetic stimulation device used for such therapy isused until it reaches a threshold temperature, and then the therapy istemporarily halted until the stimulation device cools. Such anarrangement therefore adds to the time required to perform a treatment,which is undesirable for both the patient and the health practitioner.Alternatively, a second magnetic stimulation device may need to be used(i.e., swapped with the first device when the first device reaches thethreshold temperature) so as to continue the therapy withoutinterruption while the first, overheated stimulation device cools. Thisarrangement is also undesirable because of the added expense associatedwith the purchase and maintenance of an additional magnetic stimulationdevice. Furthermore, additional time is required of the patient andhealth practitioner, as the second magnetic device will need to beset-up and/or calibrated to perform magnetic stimulation therapy on thepatient. Because the set-up and/or calibration steps provideopportunities for operator error, requiring the operator to perform suchsteps multiple times may decrease the overall safety level of thetreatment.

Conventional cooling solutions typically involve the use of air or fluidcooling mechanisms. An air cooling mechanism may involve a fan thatrapidly circulates cooled or room temperature air past the magneticdevice. A fluid cooling mechanism may involve the circulation of a coolfluid past the magnetic device, where the fluid cools the device and isheated in the process, and then to a cooling mechanism, after which thefluid is returned to the magnetic device. Both mechanisms have severaldrawbacks. For example, both mechanisms require additional moving parts(e.g., fans, cooling mechanisms such as a refrigeration or heat exchangeunit, etc.), which add to the cost and complexity of the magneticdevice. Furthermore, the additional moving parts add to the potentialfor a device malfunction.

An additional consideration of magnetic devices is acoustical noisegenerated by the magnetic coil of a magnetic device as the coil isenergized. For example, when the coil is energized, it creates a strongmagnetic field that, in many applications, rapidly changes in intensity.The changing magnetic field causes windings of the coil to experiencehoop stresses that intermittently stress the windings, which causes asharp acoustic click.

Such noise is especially pronounced in magnetic stimulation devices, asthe therapeutic magnetic fields are created by pulsing the stimulationdevice's coil. Such noise is problematic for patients, as thestimulation device is typically located in close proximity to thepatient's head, and therefore the noise from the stimulation device maybe uncomfortable. In addition, a health practitioner who is repeatedlyexposed to such noise may be adversely affected. A conventionalsolution, placing earplugs in the patient's ears, is undesirable becauseit is an additional step to perform in the therapeutic process and doesnot solve the problem of the noise caused by the device in the treatmentfacility (e.g., physician's office, hospital, etc.). In addition, theuse of earplugs is undesirable because some psychiatric or youngpatients may be uncooperative, and therefore the use of earplugsunnecessarily complicates the procedure.

Thus, a conventional solution for the reduction of acoustical noise isthe placement of noise reduction material around all or part of amagnetic device. Alternatively, a chamber containing a partial vacuummay be formed around the magnetic device, because a partial vacuumcontains very few particles that may propagate a mechanical (sound)wave. However, such noise reduction techniques have the disadvantage ofadversely affecting heat transfer for cooling. For example, the bestnoise reduction materials are fabricated to contain air pockets that donot transfer noise well. However, such air pockets also have thecharacteristic being poor conductors of heat. The same is true to aneven greater extent in the case of a vacuum. Thus, if such a noisereduction technique is used, the magnetic stimulation device cannot beadequately cooled. Attempting to mitigate such a dilemma by placingacoustical material, or forming a partial vacuum, around a coolingsystem that is itself arranged around a magnetic device is undesirablebecause of the added size, cost and complexity of the resulting device.

Conventionally, ferrofluids have been used to cool audio speakersystems, which is a lower voltage application when compared to amagnetic stimulation device or other high voltage magnetic device. Aferrofluid is a fluid with suspended ferromagnetic particles. Theferromagnetic particles can be influenced by the magnetic field createdby the speaker so as to enhance fluid convection between the speaker anda heat sink to cool the speaker. An additional benefit of ferrofluids isthat they can be used to cool a device while still performing noisereduction, because a ferrofluid typically does not support shear waves.Furthermore, a mismatch in sound velocity may also cause the reflectionof some of the sound waves.

Unfortunately, even the ferrofluid solution used in connection withspeakers has disadvantages that may render it unsuitable for use withhigh voltage magnetic devices, such as a magnetic stimulation device.For example, the ferrofluid used in connection with speaker cooling,while a dielectric when exposed to normal speaker-level voltages, may beunable to maintain dielectric isolation at the higher voltage levelsused in connection with a magnetic stimulation device. As a result,arcing or other problems may occur.

Therefore, what is needed is a ferrofluidic cooling apparatus, systemand method for high voltage applications. More particularly, what isneeded is an apparatus, system and method for convectively circulating aferrofluid to cool a high voltage magnetic device. Even moreparticularly, what is needed is an apparatus, system and method of usinga ferrofluid to cool such a high voltage magnetic device while alsomitigating acoustical noise.

SUMMARY OF THE INVENTION

In view of the foregoing shortcomings and drawbacks, an apparatus,system and method for cooling a magnetic device using a ferrofluid isdescribed. According to an embodiment, a ferrofluid chamber has ahousing that is adapted to be coupled to a component that generates amagnetic field. A ferrofluid may disposed within the housing for coolingthe component via convection of the ferrofluid that is induced by themagnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example magnetic stimulation devicein which aspects of the invention may be implemented;

FIG. 2 is a flowchart illustrating an example method of cooling amagnetic device in accordance with an embodiment of the invention; and

FIGS. 3-6 are diagrams illustrating example configurations involvingferrofluidic cooling of a magnetic device in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The subject matter of the present invention is described withspecificity to meet statutory requirements. However, the descriptionitself is not intended to limit the scope of this patent. Rather, theinventors have contemplated that the claimed subject matter might alsobe embodied in other ways, to include different steps or elementssimilar to the ones described in this document, in conjunction withother present or future technologies. Moreover, although the term “step”may be used herein to connote different aspects of methods employed, theterm should not be interpreted as implying any particular order among orbetween various steps herein disclosed unless and except when the orderof individual steps is explicitly described.

Magnetic Device Overview

As is well known to those skilled in the art, the magnitude of anelectric field induced on a conductor is proportional to the rate ofchange of magnetic flux density across the conductor. When an electricfield is induced in a conductor, the electric field creates acorresponding current flow in the conductor. The current flow is in thesame direction of the electric field vector at a given point. The peakelectric field occurs when the time rate of change of the magnetic fluxdensity is the greatest and diminishes at other times. During a magneticpulse, the current flows in a direction that tends to preserve themagnetic field (i.e., Lenz's Law).

As may be appreciated, various devices may take advantage of the aboveprinciples to induce an electric field, and such devices may be used ina variety of applications. For example, magnetic devices may be used forelectrical stimulation of the anatomy, and the like. While thediscussion herein focuses on magnetic devices that are used inconnection with magnetic stimulation of anatomical tissue, it will beappreciated that such discussion is so limited solely for purposes ofexplanation and clarity. Thus, it will be understood that an embodimentis equally applicable to any application of a magnetic device in anyfield of endeavor. Thus, the present discussion of magnetic devicesshould not be construed as limiting embodiments of the invention tomedical or other applications.

Therefore, and turning now to the context of electrical stimulation ofthe anatomy, certain parts of the anatomy (e.g., nerves, tissue, muscle,brain) act as a conductor and carry electric current when an electricfield is applied. The electric field may be applied to these parts ofthe anatomy transcutaneously by applying a time varying (e.g., pulsed)magnetic field to the portion of the body. For example, in the contextof TMS, a time-varying magnetic field may be applied across the skull tocreate an electric field in the brain tissue, which produces a current.If the induced current is of sufficient density, neuron action potentialmay be reduced to the extent that the membrane sodium channels open andan action potential response is created. An impulse of current is thenpropagated along the axon membrane that transmits information to otherneurons via modulation of neurotransmitters. Such magnetic stimulationhas been shown to acutely affect glucose metabolism and local blood flowin cortical tissue. In the case of major depressive disorder,neurotransmitter dysregulation and abnormal glucose metabolism in theprefrontal cortex and the connected limbic structures may be a likelypathophysiology. Repeated application of magnetic stimulation to theprefrontal cortex may produce chronic changes in neurotransmitterconcentrations and metabolism so that depression is alleviated.

In a similar fashion, non-cortical neurons (e.g., cranial nerves,peripheral nerves, sensory nerves) may also be stimulated by an inducedelectric field. Techniques have been developed to intentionallystimulate peripheral nerves to diagnose neuropathologies by observingresponse times and conduction velocities in response to a pulsedmagnetic field induced stimulus. Discomfort and/or pain may result ifthe induced electric field applied to a peripheral or cranial nerve isvery intense or focused on a small area of such a nerve. This discomfortmay be diminished by intentionally over-stimulating the sensory nervesin the affected nerve bundle so that they can no longer respond toexternal pain stimuli, or by reducing the intensity and focus of theinduced electric field that is causing the pain sensation.

As noted above, it should be appreciated that transcutaneous magneticstimulation is not limited to treatment of depression. In addition todepression, the transcutaneous magnetic stimulation methods andapparatus of the invention may be used to treat a patient such as ahuman suffering from epilepsy, schizophrenia, Parkinson's disease,Tourette's syndrome, amyotrophic lateral sclerosis (ALS), multiplesclerosis (MS), Alzheimer's disease, attention deficit/hyperactivitydisorder, obesity, bipolar disorder/mania, anxiety disorders (e.g.,panic disorder with and without agoraphobia, social phobia also known associal anxiety disorder, acute stress disorder and generalized anxietydisorder), post-traumatic stress disorder (one of the anxiety disordersin DSM), obsessive compulsive disorder (also one of the anxietydisorders in DSM), pain (such as, for example, migraine and trigeminalneuralgia, as well as chronic pain disorders, including neuropathicpain, e.g., pain due to diabetic neuropathy, post-herpetic neuralgia,and idiopathic pain disorders, e.g., fibromyalgia, regional myofascialpain syndromes), rehabilitation following stroke (neuro plasticityinduction), tinnitus, stimulation of implanted neurons to facilitateintegration, substance-related disorders (e.g., dependence, abuse andwithdrawal diagnoses for alcohol, cocaine, amphetamine, caffeine,nicotine, cannabis and the like), spinal cord injury andregeneration/rehabilitation, stroke, head injury, sleep deprivationreversal, primary sleep disorders (primary insomnia, primaryhypersomnia, circadian rhythm sleep disorder), cognitive enhancements,dementias, premenstrual dysphoric disorder (PMS), drug delivery systems(changing the cell membrane permeability to a drug), induction ofprotein synthesis (induction of transcription and translation),stuttering, aphasia, dysphagia, essential tremor, and/or eatingdisorders (such as bulimia, anorexia and binge eating).

Example Magnetic Stimulation Device

A ferromagnetic core may be used in connection with a magnetic device toproduce a magnetic field. In some embodiments, such a magnetic field maybe for purposes of carrying out transcutaneous magnetic stimulation suchas, for example, Transcranial Magnetic Stimulation (TMS), Repetitive TMS(rTMS), Magnetic Seizure Therapy (MST), reduction of peripheral nervediscomfort and so forth. Again, although some of the examples thatfollow may be discussed in connection with TMS and rTMS embodiments forthe purposes of explanation and clarity, any type of transcutaneousmagnetic stimulation, including all of those listed above, may beperformed according to an embodiment of the invention. In addition, andas noted above, embodiments of the invention are not limited totranscutaneous magnetic stimulation, as an embodiment may be used inconnection with magnetic devices that generate a magnetic field for anypurpose.

Furthermore, embodiments of the invention are not limited to the use offerromagnetic core magnetic stimulation devices, as other core materialsmay be used such as, for example, air. The discussion herein thereforedescribes a ferromagnetic core magnetic stimulation device solely forpurposes of explanation and clarity. In an embodiment, a ferromagneticcore may be approximately hemispherical, and in another embodiment theferromagnetic core may include a highly saturable magnetic materialhaving a magnetic saturation of at least 0.5 Tesla. In some embodiments,a ferromagnetic core may be shaped to optimize the magnetic fielddistribution in the treatment area. Treatment areas for other forms oftreatment (e.g., reduction of discomfort in peripheral nerves, etc.) maybe more or less deep than is the case for TMS.

FIG. 1 illustrates an example magnetic device 10, or “coil,” that may beused in connection with an embodiment of the invention. Device 10comprises a ferromagnetic core 12 surrounded by windings 14. Aninsulative material 16 may be interposed between core 12 and windings14. Device 10 also includes a cable 20 for connecting device 10 to acontrol system (not shown in FIG. 1 for clarity). Cable 20 may becovered by a housing 18 for protection and strain relief.

Ferromagnetic core 12 can be fabricated from various ferromagneticmaterials such as, for example, 3% grain oriented silicon steel orvanadium permendur (also known as supermendur). The material is chosento have, for example, a high saturation level, a sharp-knee B-H curve(i.e., quickly switches from saturated to non-saturated states), loweddy current losses, and a practical cost. The core material may befabricated into many electrically isolated layers to minimize eddycurrent losses. The orientation of the lamination may be such as todisrupt the eddy currents (i.e., perpendicular to the direction ofinduced current flow whenever possible). Also, if the material has agrain orientation, it may be directed parallel to the induced magneticflux. In one embodiment, the ferromagnetic core is according to U.S.Pat. Nos. 6,132,361 and 5,725,471, each of which is hereby incorporatedby reference in their entireties.

In one embodiment, patient treatment typically includes applying amagnetic field to the patient using a coil constructed with anapproximately hemispherical ferromagnetic core. The strength of thefield and switching rate is sufficient to produce stimulation of thetarget area in a manner that is appropriate to the type of treatmentbeing administered. As noted above, the generation of a magnetic fieldhaving the approximate strength for therapeutic treatment or otherpurposes also generates heat and noise. Therefore, an embodiment thatprovides an apparatus, system and method for mitigating such heat and/ornoise using a ferrofluid is discussed below.

Ferrofluidic Convection and Cooling

Generally, a ferrofluid is a suspension of small magnetic particles thatmay be, for example, approximately 10 nm in size. Such a small particlesize may be selected to assure that settling of the particles does notoccur during a time period that is appropriate for an application inwhich the ferrofluid is used. In addition, one or more surfactants maybe used to ensure continued suspension of the magnetic particles in thefluid, which may be, for example, oil, water, etc. Each particle mayhave a permanent magnetic moment, and may be comprised from magneticmaterials such as, for example, iron oxide compounds or the like. In theabsence of an external magnetic field, the magnetic moments of theindividual particles within the ferrofluid are not aligned with eachother. When a magnetic field is applied, the magnetic moments align withthe applied magnetic field. This alignment often is called“superparamagnetic” as the fluid behaves as a paramagnet with magneticmoments that are the size of the individual magnetic particles.

It will be appreciated that an increase in temperature of a ferrofluiddecreases its magnetization in an applied field. For example, at highertemperatures, the saturation moment of a ferrofluid, as well as itsinitial susceptibility, are reduced. The relationship between themagnetization of a ferrofluid and an applied magnetic field is calledthe Langevin function, which is known to those of skill in the art.

Natural convection is a phenomenon caused by the change in volume ofliquid with temperature. Hot fluids are less dense, and therefore afluid exposed to a heat source will expand and rise. Cool fluid distantfrom a heat source will move to replace the hot fluid. In this way, heatis mechanically transported away from a heat source.

In the case of ferrofluid convection, a ferrofluid is placed in amagnetic field gradient where the magnetic field is greatest. As notedabove, a cool ferrofluid has a higher magnetic susceptibility than a hotferrofluid and therefore is preferentially drawn to the areas ofgreatest magnetic field. In an embodiment, the area of the coolferrofluid greatest magnetic field may be proximate a magnetic device(e.g., a magnetic stimulation device, or the like) when such a magneticdevice is in operation. Therefore, ferrofluid that is proximate themagnetic device may be heated, which reduces the ferrofluid's magneticsusceptibility and also causes the ferrofluid to expand in volume. As aresult, cool ferrofluid (e.g., ferrofluid that is further away from themagnetic device), which has a higher magnetic susceptibility and is moredense, is drawn to the magnetic device. Thus, it will be appreciatedthat magnetic and thermal convection of the ferrofluid may beestablished by the increasing and decreasing of the magneticsusceptibility and volume of the ferrofluid. Details relating to thefabrication of ferrofluid-filled chambers is assumed to be known tothose of skill in the art, and such details are therefore omitted hereinfor clarity.

In addition, ferrofluids may be used to reduce unwanted noise insolenoids and other devices. This is because a ferrofluid is not a goodsupporter of transverse sound waves. Also, an interface between aferrofluid and an adjacent object (e.g., a magnetic device or the like)may reduce noise produced by the magnetic device. This is because of thedifference of sound velocities at such an interface, as is known to oneof skill in the art. Furthermore, the ferrofluid may provide vibrationaldamping. Thus, it will be appreciated that a ferrofluid that is beingused to cool a magnetic device may also reduce noise produced by such amagnetic device. It will be further appreciated that a ferrofluid thatis being used to cool a magnetic device may, for example, be used inconnection with other methods of sound absorption. For example, soundabsorbing material may be used to augment the sound-reducing abilitiesof the ferrofluid.

An embodiment provides a chamber containing a ferrofluid. The ferrofluidwithin the chamber may be used to cool a magnetic device substantiallyaround which the chamber may be disposed. For example, a magnetic fieldcreated by the magnetic device may induce magnetic convection of theferrofluid as discussed above. In addition, the heat generated by themagnetic device may induce thermal convection.

In one embodiment, a heat exchanger may be coupled to the chamber tocool the ferrofluid, thereby further enabling cooling of the magneticdevice as the ferrofluid circulates between the device, where theferrofluid is heated, and the heat exchanger, where the ferrofluid iscooled. Sound reduction may also be affected by the ferrofluid, as inone embodiment the chamber may be disposed around the magneticstimulation device to substantially enclose a sound-producing region ofthe device. In an embodiment, properties of the ferrofluid may beselected so as to enhance its magnetic, thermal and/or sound-mitigatingproperties.

While an embodiment discussed herein relates to Magnetic Seizure Therapy(MST) and Transcranial Magnetic Stimulation (TMS) for purposes ofexplanation and clarity, it will be appreciated that an embodiment maybe employed in connection with any type of high-voltage magnetic devicethat is used for any purpose.

Turning now to FIG. 2, a flowchart illustrating a method of cooling amagnetic device is provided. Cooling method 200 illustrated in FIG. 2begins, for example, at step 201 where a magnetic field is created. Sucha magnetic field may be created by, for example, magnetic device 10 asdiscussed above in connection with FIG. 1, or by any other type ofmagnetic device. In an embodiment, the magnetic field created at step201 may be of sufficient strength to stimulate anatomical tissue. Evenin such an embodiment, however, the magnetic field may be used for anapplication other than tissue stimulation, even though the magneticfield is of sufficient strength to do so. In an embodiment involvingTMS, for example, magnetic device 10 may operate using voltage levels ofapproximately 1,500 V or more.

At step 203, a ferrofluid is circulated. It will be appreciated that aferrofluid may be contained within a chamber, as will be discussed belowin connection with FIGS. 3-6. The ferrofluid may be circulated by way ofmagnetic convection, as was discussed in detail above, induced by themagnetic field created by, for example, magnetic device 10. In anembodiment, one on more magnetic field-creating devices may create oneor more magnetic fields to induce magnetic convection such as, forexample, in the example configuration discussed below in connection withFIG. 5. Moreover, additional components may be used to mechanicallycirculate the ferrofluid, as will be discussed below in connection withthe example configuration of FIG. 6.

At step 205, the ferrofluid is heated. Such heating may take place, forexample, proximate magnetic device 10. Such heating may occur due to theheating of such device 10 while device 10 is in operation, as wasdiscussed above. At step 207, the ferrofluid is cooled. Such cooling maytake place due to, for example, heat loss facilitated by a heatexchanger such as a heat sink, refrigeration unit or the like.Alternatively, such cooling may take place without the assistance of aheat exchanger. It will be appreciated that the heating of step 205 andthe cooling of step 207 may facilitate thermal convection of theferrofluid, as was discussed above. Such thermal convection may, in anembodiment, assist the magnetic convection of the ferrofluid discussedabove in connection with step 203.

FIG. 3 illustrates an example implementation of ferrofluidic cooling ofa magnetic device in accordance with an embodiment. Although magneticdevice 10 is illustrated as having a ferromagnetic core in FIG. 3, itwill be appreciated that magnetic device 10 may be any type of devicethat is capable of generating a magnetic field.

As can be seen in FIG. 3, chamber 36 is disposed around device 10.Contained within chamber 36 is ferrofluid 30, and disposed aroundchamber 36 is heat exchanger 32. It will be appreciated that heatexchanger 32 may be any means for cooling ferrofluid 30 including, butnot limited to, a heat sink as illustrated in connection with FIG. 3. Inaddition, in some embodiments additional components may be used inconnection with heat exchanger 32 such as, for example, a fan, arefrigeration unit or the like. Furthermore, it will be appreciated thatan embodiment may require no heat exchanger 32, as ferrofluid 30 may becooled by air surrounding chamber 36, for example.

It can be seen in FIG. 3 that sound absorber 34 is also disposed arounddevice 10 for noise-reduction purposes. Sound absorber 34 may be anymeans for reducing sound transmission, such as for examplesound-absorbing material, active noise-reduction equipment, and soforth. Thus, it will be appreciated that in some embodiments the noisereducing properties of ferrofluid 30 may be augmented with one or moresound reduction techniques.

Convection (i.e., magnetic and/or thermal convection) of ferrofluid 30is enabled as discussed above, and is represented by direction arrow A.Thus, it can be appreciated that, in an embodiment, ferrofluid 30 thatis proximate device 10 while device 10 is in operation and thereforegenerating heat is also heated. In addition, ferrofluid 30 may beattracted to device 10 because of a magnetic field generated by device10 (not shown in FIG. 3 for clarity). As noted above, the volume of aheated ferrofluid 30 increases while its magnetic susceptibilitydecreases. Therefore, ferrofluid 30 that is proximate heat exchanger 32may be cooler relative to ferrofluid 30 located proximate device 10, andas a result may be denser and may experience a stronger magnetic pull todevice 10. As may be appreciated, the heating and cooling of ferrofluid30, as well as its increasing and decreasing magnetic susceptibility,causes ferrofluid 30 to experience thermal and magnetic convection.

It should be appreciated that the example configuration depicted in FIG.3 is merely representative of any number of configurations that may beimplemented in connection with an embodiment. To illustrate this point,we turn now to FIG. 4, which depicts another example implementationaccording to an embodiment.

In FIG. 4, device 10 is again illustrated with chamber 36 disposedaround device 10. Chamber 36 further has channel 40 formed therein toconvey ferrofluid 30 to and from heat exchanger 32. The movement offerrofluid 30 to and from heat exchanger 32 is represented by directionarrow B. It will be appreciated that heat exchanger may be as describedabove in connection with FIG. 3. The configuration illustrated in FIG. 4differs from that illustrated in FIG. 3 in that sound absorber 34 isdisposed around chamber 36, rather than being used in place of chamber36 in certain locations.

FIG. 5 illustrates another example configuration according to anembodiment. Specifically, FIG. 5 illustrates a winding 54 that may bepart of magnetic device 10 (wherein device 10 is not illustrated in itsentirety in FIG. 5 for clarity) that may be used in, for example, amedical application such as MST, TMS or the like. As may be appreciated,winding 54 may be energized to cause device 10 to generate a magneticfield, which may be used to treat patient 52 and/or drive magneticconvection of ferrofluid 30, as indicated by directions arrow C. Inaddition, permanent magnet 50 may be present to induce continuous ornear-continuous convection of ferrofluid 30 (also represented bydirection arrow C). Such a configuration, in an embodiment, serves tokeep ferrofluid 30 within chamber 36 to remain relatively cool at alltimes, as ferrofluid 30 will be constantly circulating past heatexchanger 32. It will be appreciated that in some embodiments convectionof ferrofluid 30 induced by permanent magnet 50 and convection offerrofluid 30 induced by winding 54 may be additive. In other words,ferrofluid 30 may experience more powerful convection when winding 54 isenergized, for example.

Turning now to FIG. 6, another example configuration according to anembodiment is illustrated. In FIG. 6, chamber 36 is disposed proximatewinding 54 and is at least partially filled with ferrofluid 30. Magneticmaterial 62 may be positioned proximate chamber 36 and winding 54. Asmay be appreciated, magnetic material 62 may be attracted to (orrepelled from) winding 54, depending on, for example, a magnetic fieldgenerated by winding 54 and/or device 10 (not shown in FIG. 6 forclarity). In an embodiment, magnetic material 62 may be mounted on, forexample, a flexible membrane or the like to permit magnetic material 62to move within a desired area to cause ferrofluid 30 to circulatethroughout chamber 36 as indicated by direction arrow D. It will beappreciated that any such mechanical circulation induced by magneticmaterial 62 may be in addition to or in place of any of theabove-described thermal and/or magnetic convection of ferrofluid 30 thatmay be caused by a magnetic field cased by winding 54.

In addition, one-way valves 60A-B may be present to facilitate enhancedcirculation of ferrofluid 30. For example, magnetic material 62 maycause ferrofluid 30 to flow in the direction indicated by arrow D whenattracted to winding 54, but may case ferrofluid 30 to flow in anopposite direction when repelled from winding 54. Thus, one or moreone-way valves 60A-B may be operatively coupled to chamber 36 to ensurethat ferrofluid 30 only flows in the direction indicated by arrow D. Itshould be appreciated that any technique may be used to ensure suchdirectional flow of ferrofluid 30, if any is used at all, and any suchapparatus is equally consistent with an embodiment.

Therefore, it will be appreciated that magnetic material 62 acts as apumping mechanism for driving the circulation of ferrofluid 30.Alternate embodiments may use other such pumping mechanisms, and suchembodiments are in no way limited to the use of magnetic material 62,which is presented herein merely as an illustrative example. Forexample, a fluid pump may be operatively coupled to chamber 36 tocirculate ferrofluid 30, and such a configuration would remainconsistent with an embodiment. In addition, such a fluid pump (or asecond fluid pump) may also circulate an additional, non-ferrofluid foradditional cooling or other purposes. Thus, any type of pumpingmechanism may be employed to circulate ferrofluid 30, and any suchpumping mechanism may operate to augment or replace the aforementionedmagnetic and/or thermal convection of ferrofluid 30.

It is to be understood that the foregoing illustrative embodiments havebeen provided merely for the purpose of explanation and are in no way tobe construed as limiting of the invention. Words used herein are wordsof description and illustration, rather than words of limitation. Inaddition, the advantages and objectives described herein may not berealized by each and every embodiment practicing the present invention.Further, although the invention has been described herein with referenceto particular structure, materials and/or embodiments, the invention isnot intended to be limited to the particulars disclosed herein. Rather,the invention extends to all functionally equivalent structures, methodsand uses, such as are within the scope of the appended claims. Thoseskilled in the art, having the benefit of the teachings of thisspecification, may affect numerous modifications thereto and changes maybe made without departing from the scope and spirit of the invention.

1. A ferrofluid chamber, comprising: a housing adapted to be coupled to a component that generates a magnetic field of sufficient strength to stimulate anatomical tissue; and a ferrofluid disposed within the housing for cooling the component, wherein the chamber is configured to facilitate thermal and magnetic convection of the ferrofluid.
 2. The chamber of claim 1, wherein the housing is further adapted to enable convection of the ferrofluid when in the presence of the magnetic field.
 3. The chamber of claim 1, wherein the housing is disposed around the component so as to substantially enclose an acoustic noise-producing region of the component.
 4. The chamber of claim 1, wherein the ferrofluid contained within the chamber and the component form a first noise-attenuating interface.
 5. The chamber of claim 1, wherein the ferrofluid is resistant to shear sound waves.
 6. The chamber of claim 1, further comprising a heat exchanger coupled to the housing for cooling the ferrofluid.
 7. The chamber of claim 6, wherein the heat exchanger is a heat sink.
 8. The chamber of claim 6, wherein the housing is configured to facilitate thermal and magnetic convection of the ferrofluid between the component and the heat exchanger.
 9. The chamber of claim 6, further comprising a pumping mechanism to cause the ferrofluid to circulate between the component and the heat exchanger.
 10. The chamber of claim 6, wherein the pumping mechanism is a magnetic material for causing circulation of the ferrofluid when in the presence of the magnetic field.
 11. The chamber of claim 6, wherein the ferrofluid contained within the chamber and the heat exchanger form a second noise-attenuating interface.
 12. The chamber of claim 1, wherein the component is a coil.
 13. The chamber of claim 12, wherein the coil has a ferromagnetic core.
 14. The chamber of claim 12, wherein the coil has an air core.
 15. The chamber of claim 1, wherein the component stimulates human brain tissue in connection with transcranial magnetic stimulation or magnetic seizure therapy.
 16. The chamber of claim 1, wherein the magnetic field is a first magnetic field, and further comprising a permanent magnet proximate the housing to create a second magnetic field, wherein the ferrofluid experiences magnetic convection when exposed to the second magnetic field.
 17. A magnetic stimulation system for generating a magnetic field having sufficient strength to stimulate anatomical tissue, comprising: a component for generating the magnetic field of sufficient strength to stimulate anatomical tissue; a chamber disposed substantially around the component, the chamber comprising a housing adapted to be coupled to the component that generates the magnetic field and a ferrofluid disposed within the housing for cooling the component; a heat exchanger for cooling the ferrofluid, wherein the chamber is configured to facilitate thermal and magnetic convection of the ferrofluid between the component and the heat exchanger.
 18. The system of claim 17, wherein the magnetic field generated by the component drives the magnetic convection of the ferrofluid.
 19. The system of claim 17, wherein the chamber is disposed around the component so as to substantially enclose an acoustic noise-producing region of the component.
 20. The system of claim 17, wherein the ferrofluid is resistant to shear sound waves.
 21. The system of claim 17, wherein the ferrofluid contained within the chamber and the magnetic device form a first noise-attenuating interface.
 22. The system of claim 17, wherein the ferrofluid contained within the chamber and the heat exchanger form a second noise-attenuating interface.
 23. The system of claim 17, wherein the component is a coil.
 24. The system of claim 23, wherein the coil has a ferromagnetic core.
 25. The system of claim 23, wherein the coil has an air core.
 26. The system of claim 17, further comprising a magnetic material for causing circulation of the ferrofluid in a first direction when in the presence of the magnetic field.
 27. The system of claim 26, further comprising a valve for preventing the ferrofluid from circulating in a second direction.
 28. The system of claim 17, wherein the heat exchanger is a heat sink.
 29. The system of claim 17, wherein the component is used for stimulating tissue in connection with transcranial magnetic stimulation or magnetic seizure therapy.
 30. The system of claim 17, wherein the magnetic field is a first magnetic field, and further comprising a permanent magnet to create a second magnetic field, wherein the ferrofluid experiences magnetic convection when exposed to the second magnetic field.
 31. The system of claim 17, further comprising a pumping mechanism to circulate the ferrofluid between the component and the heat exchanger.
 32. The system of claim 31, wherein the pumping mechanism is activated by a pulsing magnetic field causing circulation of the ferrofluid in a first direction when in the presence of the magnetic field.
 33. The system of claim 32, further comprising a valve for preventing the ferrofluid from circulating in a second direction. 